Porous, electrically conductive fluid distribution plate for fuel cells

ABSTRACT

In at least one embodiment, the present invention provides an electrically conductive fluid distribution plate and a method of making, and system for using, the electrically conductive fluid distribution plate. In at least one embodiment, the plate comprises a plate body defining a set of fluid flow channels configured to distribute flow of a fluid across at least one side of the plate, and a polymeric porous conductive layer proximate the plate body, with the porous conductive layer having a porosity sufficient to result in a water contact angle of the surface of less than 40°.

FIELD OF THE INVENTION

The present invention relates generally to a porous electricallyconductive fluid distribution plate, a method of making a porouselectrically conductive fluid distribution plate, and systems using aporous electrically conductive fluid distribution plate according to thepresent invention. More specifically, the present invention is relatedto the use of a porous electrically conductive fluid distribution platein addressing water transport difficulties in fuel cells and other typesof devices.

BACKGROUND ART

Fuel cells are being developed as a power source for many applicationsincluding vehicular applications. One such fuel cell is the protonexchange membrane or PEM fuel cell. PEM fuel cells are well known in theart and include in each cell thereof a membrane electrode assembly orMEA. The MEA is a thin, proton-conductive, polymeric,membrane-electrolyte having an anode electrode face formed on one sidethereof and a cathode electrode face formed on the opposite sidethereof. One example of a membrane-electrolyte is the type made from ionexchange resins. An exemplary ion exchange resin comprises aperfluoronated sulfonic acid polymer such as NAFION™ available from theE.I. DuPont de Nemeours & Co. The anode and cathode faces, on the otherhand, typically comprise finely divided carbon particles, very finelydivided catalytic particles supported on the internal and externalsurfaces of the carbon particles, and proton conductive particles suchas NAFION™ intermingled with the catalytic and carbon particles; orcatalytic particles, without carbon, dispersed throughout apolytetrafluorethylene (PTFE) binder.

Multi-cell PEM fuel cells comprise a plurality of the MEAs stackedtogether in electrical series and separated one from the next by agas-impermeable, electrically-conductive fluid distribution plate knownas a separator plate or a bipolar plate. Such multi-cell fuel cells areknown as fuel cell stacks. The bipolar plate has two working faces, oneconfronting the anode of one cell and the other confronting the cathodeon the next adjacent cell in the stack, and electrically conductscurrent between the adjacent cells. Electrically conductive fluiddistribution plates at the ends of the stack contact only the end cellsand are known as end plates. The bipolar plates contain a flow fieldthat distributes the gaseous reactants (e.g. H₂ and O₂/air) over thesurfaces of the anode and the cathode. These flow fields generallyinclude a plurality of lands which define therebetween a plurality offlow channels through which the gaseous reactants flow between a supplyheader and an exhaust header located at opposite ends of the flowchannels.

A highly porous (i.e. ca. 60% to 80%), electrically-conductive material(e.g. cloth, screen, paper, foam, etc.) known as “diffusion media” isgenerally interposed between electrically conductive fluid distributionplates and the MEA and serves (1) to distribute gaseous reactant overthe entire face of the electrode, between and under the lands of theelectrically conductive fluid distribution plate, and (2) collectscurrent from the face of the electrode confronting a groove, and conveysit to the adjacent lands that define that groove. One known suchdiffusion media comprises a graphite paper having a porosity of about70% by volume, an uncompressed thickness of about 0.17 mm, and iscommercially available from the Toray Company under the name Toray 060.Such diffusion media can also comprise fine mesh, noble metal screen andthe like as is known in the art.

In an H₂—O₂/air PEM fuel cell environment, the electrically conductivefluid distribution plates can typically be in constant contact withmildly acidic solutions (pH 3-5) containing F⁻, SO₄ ⁻⁻, SO₃ ⁻, HSO₄ ⁻,CO₃ ⁻⁻, and HCO₃ ⁻, etc. Moreover, the cathode typically operates in ahighly oxidizing environment, being polarized to a maximum of about +1 V(vs. the normal hydrogen electrode) while being exposed to pressurizedair. Finally, the anode is typically constantly exposed to hydrogen.Hence, the electrically conductive fluid distribution plates should beresistant to a hostile environment in the fuel cell.

One of the more common types of suitable electrically conductive fluiddistribution plates include those molded from polymer compositematerials which typically comprise 50% to 90% by volumeelectrically-conductive filler (e.g. graphite particles or filaments)dispersed throughout a polymeric matrix (thermoplastic or thermoset).Recent efforts in the development of composite electrically conductivefluid plates have been directed to materials having adequate electricaland thermal conductivity. Material suppliers have developed high carbonloading composite plates comprising graphite powder in the range of 50%to 90% by volume in a polymer matrix to achieve the requisiteconductivity targets. Plates of this type will typically be able towithstand the corrosive fuel cell environment and, for the most part,meet cost and conductivity targets. One such currently available bipolarplate is available as the BMC plate from Bulk Molding Compound, Inc. ofWest Chicago, Ill.

Alternatively, discrete conductive fibers have been used in compositeplates in an attempt to reduce the carbon loading and to increase platetoughness. See copending U.S. Pat. No. 6,607,857 to Blunk, et. al.,issued Aug. 19, 2003 which is assigned to the assignee of thisinvention, and is incorporated herein by reference. Fibrous materialsare typically ten to one thousand times more conductive in the axialdirection as compared to conductive powders. See U.S. Pat. No. 6,827,747to Lisi, et. al., issued Dec. 7, 2004 which is assigned to the assigneeof the present invention and is incorporated herein by reference.

Another one of the more common types of suitable electrically conductivefluid distribution plates include those made of metal coated withpolymer composite materials containing about 30% to about 40% by volumeconductive particles. In this regard, see U.S. Pat. No. 6,372,376 toFronk et al., issued Apr. 16, 2002, which (1) is assigned to theassignee of this invention, (2) is incorporated herein by reference, and(3) discloses electrically conductive fluid distribution plates madefrom metal sheets coated with a corrosion-resistant,electrically-conductive layer comprising a plurality of electricallyconductive, corrosion-proof (i.e. oxidation-resistant and-acidresistant) filler particles dispersed throughout a matrix of anacid-resistant, water insoluble, oxidation-resistant polymer that bindsthe particles together and to the surface of the metal sheet. Fronk etal-type composite coatings will preferably have a resistivity no greaterthan about 50 ohm-cm and a thickness between about 5 microns and 75microns depending on the composition, resistivity and integrity of thecoating. The thinner coatings are preferred to achieve lower IR dropthrough the fuel cell stack.

As discussed above, a great percentage of the electrically conductivefluid distribution plates comprise either a conductive polymericcomposite material or a metallic base layer coated with a conductivepolymer composite material. While these types of plates currently haveacceptable water management properties, there is a desire to provide anelectrically conductive fluid distribution plate having increased watermanagement properties.

SUMMARY OF THE INVENTION

In at least one embodiment, an electrically conductive fluiddistribution plate is provided comprising a plate body defining a set offluid flow channels configured to distribute flow of a fluid across atleast one side of the plate, and a polymeric porous conductive layerproximate the plate body having a porosity sufficient to result in awater contact angle of the surface of less than 40°.

In yet another embodiment, a method of manufacturing a fluiddistribution plate is provided comprising providing a plate body havinga body defining a set of fluid flow channels configured to distributeflow of a fluid across at least one side of the plate, and providing apolymeric porous conductive layer on the body having a porositysufficient to result in a water contact angle of less than 40°.

In still yet another embodiment, a fuel cell is provided. In at leastone embodiment, the fuel cell comprises a first electrically conductivefluid distribution plate comprising a plate body defining a set of fluidflow channels configured to distribute flow of a fluid across at leastone side of the plate, and a polymeric porous conductive layer proximatethe plate body having a porosity sufficient to result in a water contactangle of the surface of less than 40°. The fuel cell further includes asecond electrically conductive fluid distributing plate, and a membraneelectrode assembly separating the first electrically conductive fluiddistribution plate and the second electrically conductive fluiddistribution plate. The membrane electrode assembly comprises anelectrolyte membrane, having a first side and a second side, an anodeadjacent to the first side of the electrolyte membrane, and a cathodeadjacent to the second side of the electrolyte membrane.

The present invention will be more fully understood from the followingdescription of preferred embodiments of the invention taken togetherwith the accompanying drawings. It is noted that the scope of the claimsis defined by the recitations therein and not by the specific discussionof features and advantages set forth in the present description.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description of the embodiments of the presentinvention can be best understood when read in conjunction with thefollowing drawings, where like structure is indicated with likereference numerals and in which:

FIG. 1 is a schematic illustration of a vehicle including a fuel cellsystem;

FIG. 2 is a schematic illustration of a fuel cell stack employing twofuel cells;

FIG. 3 is an illustration of an electrically conductive fluiddistribution plate according to one embodiment of the present invention;and

FIG. 4 is an illustration of an electrically conductive fluiddistribution plate according to another embodiment of the presentinvention.

Skilled artisans appreciate that elements in the figures are illustratedfor simplicity and clarity and have not necessarily been drawn to scale.For example, the dimensions of some of the elements in the figures maybe exaggerated relative to other elements to help to improveunderstanding of embodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiments is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses. Reference will now be made in detail topresently preferred compositions, embodiments and methods of the presentinvention, which constitute the best modes of practicing the inventionpresently known to the inventors. The figures are not necessarily toscale. However, it is to be understood that the disclosed embodimentsare merely exemplary of the invention that may be embodied in variousand alternative forms. Therefore, specific details disclosed herein arenot to be interpreted as limiting, but merely as a representative basesfor the claims and/or as a representative basis for teaching one skilledin the art to variously employ the present invention.

Except in the examples, or where otherwise expressly indicated, allnumerical quantities in this description indicating amounts of materialor conditions of reaction and/or use are to be understood as modified bythe word “about” in describing the broadest scope of the invention.Practice within the numerical limits stated is generally preferred.Also, unless expressly stated to the contrary: percent, “parts of”, andratio values are by weight; the term “polymer” includes “oligomer”,“copolymer”, “terpolymer”, and the like; the description of a group orclass of materials as suitable or preferred for a given purpose inconnection with the invention implies that mixtures of any two or moreof the members of the group or class are equally suitable or preferred;description of constituents in chemical terms refers to the constituentsat the time of addition to any combination specified in the description,and does not necessarily preclude chemical interactions among theconstituents of a mixture once mixed; the first definition of an acronymor other abbreviation applies to all subsequent uses herein of the sameabbreviation and to normal grammatical variations of the initiallydefined abbreviation; and, unless expressly stated to the contrary,measurement of a property is determined by the same technique aspreviously or later referenced for the same property.

Referring to FIG. 1, an exemplary fuel cell system 2 for automotiveapplications is shown. It is to be appreciated, however, that other fuelcell system applications, such as for example, in the area ofresidential systems, may benefit from the present invention.

In the embodiment illustrated in FIG. 1, a vehicle is shown having avehicle body 90, and an exemplary fuel cell system 2 having a fuel cellprocessor 4 and a fuel cell stack 15. A discussion of embodiments of thepresent invention as embodied in a fuel cell stack and a fuel cell, isprovided hereafter in reference to FIGS. 2-6. It is to be appreciatedthat while one particular fuel cell stack 15 design is described, thepresent invention may be applicable to any fuel cell stack designs wherefluid distribution plates have utility.

FIG. 2 depicts a two fuel cell, fuel cell stack 15 having a pair ofmembrane-electrode-assemblies (MEAs) 20 and 22 separated from each otherby an electrically conductive fluid distribution plate 30. Plate 30serves as a bi-polar plate having a plurality of fluid flow channels 35,37 for distributing fuel and oxidant gases to the MEAs 20 and 22. By“fluid flow channel” we mean a path, region, area, or any domain on theplate that is used to transport fluid in, out, along, or through atleast a portion of the plate. The MEAs 20 and 22, and plate 30, may bestacked together between clamping plates 40 and 42, and electricallyconductive fluid distribution plates 32 and 34. In the illustratedembodiment, plates 32 and 34 serve as end plates having only one sidecontaining channels 36 and 38, respectively, for distributing fuel andoxidant gases to the MEAs 20 and 22, as opposed to both sides of theplate.

Nonconductive gaskets 50, 52, 54, and 56 may be provided to provideseals and electrical insulation between the several components of thefuel cell stack. Gas permeable carbon/graphite diffusion papers 60, 62,64, and 66 can press up against the electrode faces of the MEAs 20 and22. Plates 32 and 34 can press up against the carbon/graphite papers 60and 66 respectively, while the plate 30 can press up against thecarbon/graphite paper 64 on the anode face of MEA 20, and againstcarbon/graphite paper 60 on the cathode face of MEA 22.

In the illustrated embodiment, an oxidizing fluid, such as O₂, issupplied to the cathode side of the fuel cell stack from storage tank 70via appropriate supply plumbing 86. While the oxidizing fluid is beingsupplied to the cathode side, a reducing fluid, such as H₂, is suppliedto the anode side of the fuel cell from storage tank 72, via appropriatesupply plumbing 88. Exhaust plumbing (not shown) for both the H₂ andO₂/air sides of the MEAs will also be provided. Additional plumbing 80,82, and 84 is provided for supplying liquid coolant to the plate 30 andplates 32 and 34. Appropriate plumbing for exhausting coolant from theplates 30, 32, and 34 is also provided, but not shown.

FIG. 3 illustrates an exemplary electrically conductive fluiddistribution plate 30 comprising a first sheet 102 and a second sheet104. First and second sheets 102, 104 comprise a plurality of fluid flowchannels 106, 108 on their exterior sides/surfaces through which thefuel cell's reactant gases flow typically in a tortuous path along oneside of each plate. The interior sides of the first and second sheets102, 104 may include a second plurality fluid flow channels 110, 112through which coolant passes during the operation of the fuel cell. Whenthe interior sides of first sheet 102 and second sheet 104 are placedtogether to form a plate body 120, the fluid flow channels connect andform a series of channels for coolant to pass through the plate 30.

The plate body 120 may be formed from a single sheet, or plate, ratherthan the two separate sheets illustrated in FIG. 3. When the plate body120 is formed from a single plate, the channels may be formed on theexterior sides of the plate body 120 and through the middle of the platebody 120 such that the resulting plate body 120 is equivalent to theplate body 120 configured from two separate sheets 102, 104.

The plate body 120 may be formed from a metal, a metal alloy, or acomposite material, and has to be conductive. In one embodiment, apassivating metal or a passivating alloy forms the plate body 120. By“passivating metal” or “passivating alloy” we mean a metal or an alloythat forms an inactive passivating layer as a result of reaction withambient substances such as air or water. For example, the passivatinglayer (not shown) may be a metal oxide. Metal oxides typically act asbarriers to further oxidation by requiring oxygen to diffuse through thelayer to reach the metal or alloy surface. Thus, the passivating layercan protect the integrity of the metal or metal alloy.

Suitable metals, metal alloys, and composite materials should becharacterized by sufficient durability and rigidity to function as afluid distribution plate in a fuel cell. Additional design propertiesfor consideration in selecting a material for the plate body include gaspermeability, conductivity, density, thermal conductivity, corrosionresistance, pattern definition, thermal and pattern stability,machinability, cost and availability.

Available metals and alloys include aluminum, titanium, stainless steel,nickel based alloys, and combinations thereof. Composite materials maycomprise graphite, graphite foil, graphite particles in a polymermatrix, carbon fiber paper and polymer laminates, polymer plates withmetal cores, conductively coated polymer plates, and combinationsthereof.

First and second sheets 102, 104 are typically between about 51 to about510: (microns) thick. The sheets 102, 104 may be formed by machining,molding, cutting, carving, stamping, photo etching such as through aphotolithographic mask, chemical etching or any other suitable designand manufacturing process. It is contemplated that the sheets 102, 104may comprise a laminate structure including a flat sheet and anadditional sheet including a series of exterior fluid flow channels. Aninterior metal spacer sheet (not shown) may be positioned between thefirst and second sheets 102, 104.

In the schematically illustrated plate 30 of FIG. 3, the substrate 102,104 forming the structural component of the body 120 comprises acorrosion-susceptible metal such as aluminum, titanium, stainless steel,and nickel based alloys. The working faces of the plate 30 are coveredwith a conductive polymeric composite coating 125. In at least oneembodiment, the polymeric conductive coating 125 comprises anelectrically-conductive, oxidation resistant, and acid-resistantprotective material having a resistivity less than about 50 ohm-cm², andcomprises a plurality of oxidation-resistant, acid-insoluble, conductiveparticles (i.e. less than about 50 microns) dispersed throughout anacid-resistant, oxidation-resistant polymer matrix. Any suitableconductive polymeric coating 125 may be employed. Suitable examples ofsuch coatings and their manner of application can be found in U.S. Pat.No. 6,372,376.

In at least one embodiment, the conductive filler particles can be atleast one of gold, platinum, graphite, carbon, palladium, niobium,rhodium, ruthenium, and the rare earth metals. In at least certainembodiments, the particles may comprise conductive carbon and graphiteat a loading of 25% by weight. The polymer matrix may comprise anywater-insoluble polymer that can be formed into a thin adherent film andthat can withstand the hostile oxidative and acidic environment of thefuel cell. Hence, such polymers, as epoxies, polyamide-imides,polyether-imides, polyphenols, fluro-elastomers (e.g., polyvinylideneflouride), polyesters, phenoxy-phenolics, epoxide-phenolics, acrylics,and urethanes, inter alia are seen to be useful with the compositecoating. Cross-linked polymers may be employed for producing impermeablecoatings, with polyamide-imide thermosetting polymers being mostpreferred.

In at least one embodiment, the polymer composite layer 125 may beapplied by dissolving polyamide-imide in a solvent comprising a mixtureof N-methylpyrrolidone, propylene glycol and methyl ether acetate, and21% to 23% by weight of a mixture of graphite and carbon black particlesadded thereto. In at least one embodiment, the graphite particles mayrange in size from 5 microns to 20 microns and the carbon blackparticles may range in size from 0.5 micron to 1.5 microns. In at leastone embodiment, the mix may be sprayed on to the substrate, dried (i.e.solvent vaporized), and cured to provide 10 to 30 micron thick coatinghaving a carbon-graphite content of 38% by weight. It may be curedslowly at low temperatures (i.e. <400° F.), or more quickly in a twostep process wherein the solvent is first removed by heating for tenminutes at about 300° F. to 350° F. (i.e., dried) followed by highertemperature heating (500° F. to 750° F.) for various times ranging fromabout ½ min to about 15 min (depending on the temperature used) to curethe polymer. As described hereinafter, the porous surface layer 130 ofthe invention is applied before drying and curing while the compositelayer 125 is still tacky.

The conductive polymer coating 125 may be applied directly to thesubstrate metal and allowed to dry/cure thereon, or the substrate metal(e.g., Al) may first be covered with an oxidizable metal (e.g.,stainless steel) before the electrically conductive polymer compositelayer 125 is applied (see Li et al. supra). The composite layer 125 maybe applied in a variety of ways, e.g., brushing, spraying, spreading, orlaminating a preformed film onto the substrate.

In the embodiment illustrated in FIG. 3, the electrically conductivefluid distribution plate 30 includes a porous conductive coating 130adhered to and covering polymeric conductive coating 125. In at leastone embodiment, the porous conductive coating 130 has a level ofporosity suitable to result in a water contact angle of less than 40°,in another embodiment of less than 25°, in yet another embodiment ofless than 10°, in still yet another embodiment of less than 5°, and instill yet another embodiment of less than 1°. While porous conductivecoating 130 can extend over substantially the entire outer surface ofplate 30, as schematically illustrated in FIG. 3, the porous conductivecoating 130 can also extend over less than the entire outer surface.

Applicants have found that providing an electrically conductivedistribution plate 30 having the porous conductive layer 130 with aporosity (in percent by volume) of at least 10% can result in anelectrically conducted distribution plate having excellent watermanagement properties. In at least one embodiment, the porous conductivelayer 130 is substantially similar to the polymeric conductive coating125 described above except that the porous conductive coating is moreporous. In at least one embodiment, the porous conductive coating 130 ofthe electrically conductive fluid distribution plate 30 made inaccordance with the present invention may exhibit a porosity of 10 to50%, in other embodiments between 15 and 40%, and in yet otherembodiments between 20 and 35%. Porosity may be measured by the BETsurface area measurement technique.

In at least one embodiment, porous conductive layer 130 of theelectrically conductive fluid distribution plate 30 made in accordancewith the present invention may exhibit a pore density of 50 to 3000pores per cm of surface area, in other embodiments between 100 and 1000pores per cm of surface area, and in yet other embodiments between 250and 750 pores per cm of surface area. Pore density may be measured bythe BET surface area measurement technique.

In at least one embodiment, the porous conductive layer 130 of theelectrically conductive fluid distribution plate 30 made in accordancewith the present invention may exhibit an average pore diameter of 0.05to 1 microns, in other embodiments between 0.1 and 0.5 microns. Averagepore diameter may be measured by scanning electron microscopy.

The electrically conductive fluid distribution plate 30 of the presentinvention can be made by providing the porous conductive layer 130 ofthe plate 30 having at least one of the porosity ranges discussed above.The average porosity of the surface of a conventional plate is typicallybelow 5% and has a water contact angle of above 80°.

The manner in which the desired level of porosity of the porousconductive layer 130 is achieved is not necessarily important. Theporous conductive layer 130 can be provided in any suitable manner, suchas chemically or mechanically. One exemplary manner is to provide a wetlayer of polymeric conductive coating of the same or similar compositionas used to form conductive polymeric composite coating 125 overconductive polymeric composite coating 125. The wet polymeric conductivelayer can be provided in any suitable manner such as by spraying. Priorto the wet polymeric conductive layer fully drying, a suitable poreproducing agent can be embedded within the wet polymeric conductivelayer. The pore producing agent can be embedded in any suitable manner,such as by spraying, Doctor Blade coating, and screen printing.

The wet polymeric layer with the pore producing agent embedded withincan then be dried or cured. If excess pore producing agent is remainingon the surface of the cured polymeric layer with the pore producingagent embedded therein after curing, the surface layer can be wiped orcleaned of the excess pore producing agent in any suitable manner. Afterthe wet polymeric conductive layer is cured, the suitable pore producingagent can be exposed to a removal media to cause the pore producingagent to form pores within the conductive polymeric layer to form aporous conductive coating 130. Any suitable amount of pore producingagent can be added to wet polymeric conductive layer to result in theporous conductive coating 130 having the desired porosity.

In at least certain embodiments, the pore producing agent can be anysuitable pore producing agent, such as a pore forming agent, a foamingagent, and mixtures thereof. In at least one embodiment, the removalmedia can be any suitable media, such as heat, and solvent for removingthe pore producing agent to form pores in the coating 130.

In at least one embodiment, the pore producing agent is in the form of asolid granular pore forming agent with a predetermined particlediameter, such as 0.1 to 10 microns. Some examples of suitable poreforming agents include, but are not necessarily limited to, any suitableinorganic salt such as carbonates and bicarbonates. Some examples ofsuitable carbonates include, but are not necessarily limited to sodiumcarbonate, potassium carbonate, ammonium carbonate, magnesium carbonate,calcium carbonate, sodium bicarbonate, potassium bicarbonate, ammoniumbicarbonate, magnesium bicarbonate, calcium bicarbonate, zinc carbonate,barium carbonate, and mixtures thereof.

Some examples of other suitable pore forming agents include nitrites,such as sodium nitrites.

Some examples of other suitable pore forming agents include certainorganic pore forming compounds such as camphor, urea and derivatives ofcamphor or urea, and mixtures thereof.

Examples of suitable solvent removal medias include, but are notnecessarily limited to, acid, water and bases.

In at least one embodiment, the pore producing agent comprises a foamingagent. Any suitable foaming agent and process may be used. Suitablefoaming agents include physical and chemical foaming agents, such as azocompounds, azodicarbonamide, hydrazines, such as trihydrazinotriazine,tetrazoles, such as 5-phenyltetrazole, benzoxazines and semicarbazides.

In another embodiment, the pore surface layer 130 could be formed byforming pores in the outer surface layer 130 after it has been cured andformed. In this embodiment, pins or other protrusions could bepenetrated into a heated and/or softened layer 130 to form porestherein. In this embodiment, the pins or protrusions may also be heatedeither in addition to, or in lieu of, heating the layer 130.

In at least one embodiment, when a lower contact resistance is desired,the pore producing agent can be mixed with a conductive material such asgraphite, gold, platinum, carbon, palladium, niobium, rhodium, rutheniumand the rare earth metals. In this embodiment, the mixture of the poreproducing agent and the conductive material could be in any suitableproportion. However, it is anticipated that a 75/25 mixture of poreproducing agent and conductive material to a 25/75 mixture of poreproducing agent and conductive material is likely to find utility. In atleast one embodiment, a particularly preferred mixture comprises a 50/50mixture of graphite (superior graphite BG-34) and sodium carbonate.

FIG. 4 illustrates another embodiment of the present invention. Theplate 30′ and body 120′ illustrated in FIG. 4 are similar inconstruction and use to the plate 30 and body 120 illustrated in FIG. 3.Parts of the plate 30′ that are substantially the same as thecorresponding parts in the plate 30 illustrated in FIG. 3 are given thesame reference numeral and parts of the plate 30′ that are substantiallydifferent than the corresponding parts in the plate 30 are given thesame part number with the suffix “′” (prime) added for clarity.

The body 120′ of the electrically conductive fluid distribution plate30′ is made (e.g. molded) entirely of composite material, and the poroussurface layer 130 is formed on the exterior surface of the compositethat engages the diffusion media. In this embodiment, conductive coating125 is not necessary. The composite material of the plate 30′ can be anysuitable conductive composite material for forming plates, such as apolymer composite material comprising 50% to 90% by volumeelectrically-conductive filler (e.g. graphite particles or filaments)dispersed throughout a polymeric matrix (thermoplastic or thermoset).

In another embodiment, the porous surface layer 130 could be formed bymolding the composite plate 30′ in a textured mold that would render theexterior surface of the composite plate 30′ with the desired porosity.In this embodiment, when employing the use of a textured mold, theporous layer 130 can extend into the composite plate body 120′ to adepth of 1 to 5 micrometers.

An electrically conductive fluid distribution plate according to thevarious embodiments of the present invention has excellent watermanagement properties. It should be understood that the principles ofthe present invention apply equally as well to unipolar plates andbipolar plates.

The present invention will be further explained by way of example. It isto be appreciated that the present invention is not limited by theexample.

EXAMPLE

A metal bipolar plate is first coated with a conductive protectivepolymeric coating such as those disclosed in U.S. Pat. No. 6,372,376.This first coating helps to protect the underlying metal (e.g. stainlesssteel) from corroding in the aggressive fuel cell environment and isflashed for 10 minutes at 150° C. and then cured at 260° C. for 15minutes. After the plate cools down, a second layer of the samepolymeric coating is then sprayed onto the first coating. This wet layeris then dusted with a mixture (50/50 by weight) of graphite (e.g.superior graphite BG-34) and sodium carbonate and is then cured usingthe same curing cycle as the first coating. After curing, dry extra dust(graphite and sodium carbonate) is wiped off the plate. The coated plateis then dipped in an acidic solution of 0.1 M H₂SO₄ to dissolve thesodium carbonate particles that are embedded in the top layer, evolvinggases (e.g. CO₂) that forms pores inside the top layer. The plate isthen washed and dried to remove any salt that might remain on thesurface as a result of the dissolution of the sodium carbonate. Theexterior coating has a porosity of >30% as measured by BET measurementtechniques. The water contact angle on this plate is measured to be lessthan 10°.

While embodiments of the invention have been illustrated and described,it is not intended that these embodiments illustrate and describe allpossible forms of the invention. Rather, the words used in thespecification are words of description rather than limitation, and it isunderstood that various changes may be made without departing from thespirit and scope of the invention.

1. An electrically conductive fluid distribution plate comprising: aplate body defining a set of fluid flow channels configured todistribute flow of a fluid across at least one side of the plate; and apolymeric porous conductive layer proximate to the plate body, theporous conductive layer having a porosity sufficient to result in awater contact angle of the surface of less than 40°.
 2. The plate ofclaim 1 wherein the porous conductive layer comprises a porousconductive coating adhered to the plate body, the porous conductivecoating having a porosity of at least 10%.
 3. The plate of claim 2wherein the coating has a pore density of at least 50 pores per cm ofsurface area of the coating.
 4. The plate of claim 3 wherein the poreshave an average size of 0.05 to 1.0 microns.
 5. The plate of claim 4wherein the plate body comprises a metallic sheet and a compositepolymeric conductive coating, different from the porous conductivecoating.
 6. The plate of claim 1 wherein the plate body comprises acomposite comprising electrically conductive filler disposed throughouta polymeric matrix.
 7. The plate of claim 2 wherein the water contactangle is less than 25°.
 8. The plate of claim 2 wherein the porosity ofthe coating is 10 to 50%.
 9. The plate of claim 1 wherein the platecomprises a bipolar plate.
 10. The plate of claim 2 wherein the porosityof the coating was obtained by disposing a solid pore forming agent in aconductive coating and exposing the pore forming agent to an acidsufficient to dissolve the foaming agent.
 11. The plate of claim 10wherein the pore forming agent comprises sodium carbonate.
 12. The plateof claim 6 wherein the porosity of the layer was obtained by moldingpores into the body.
 13. A method of manufacturing a fluid distributionplate comprising: providing a plate body having a body defining a set offluid flow channels configured to distribute flow of a fluid across atleast one side of the plate; and providing a polymeric porous conductivelayer on the body, the porous conductive layer having a porositysufficient to result in a water contact angle of less than 40°.
 14. Themethod of claim 13 wherein the step of providing a porous conductivelayer on the body comprises: providing a conductive polymeric coatinghaving a pore forming agent embedded thereon over the body; and exposingthe pore producing agent to a removal media to cause the pore producingagent to produce pores in the conductive polymeric coating to provide aporous conductive coating on the plate body with a water contact angleof less than 40°.
 15. The method of claim 14 wherein the removal mediacomprises acid.
 16. The method of claim 15 wherein the pore producingagent comprises sodium carbonate.
 17. The method of claim 16 wherein thepore producing agent further comprises graphite.
 18. The method of claim13 wherein the body comprises a conductive composite material, and theporosity is created by molding pores into the composite plate.
 19. Themethod of claim 14 wherein the removal media comprises a non-chemicaltreating media and the pore producing agent comprises a foaming agent.20. A fuel cell comprising: a first electrically conductive fluiddistribution plate comprising a plate body defining a set of fluid flowchannels configured to distribute flow of a fluid across at least oneside of the plate, a polymeric porous conductive layer proximate theplate body, the porous conductive layer having a porosity sufficient toresult in a water contact angle of the surface of less than 40°, asecond electrically conductive fluid distributing plate; and a membraneelectrode assembly separating the first electrically conductive fluiddistribution plate and the second electrically conductive fluiddistribution plate, the membrane electrode assembly comprising: anelectrolyte membrane, having a first side and a second side, an anodeadjacent to the first side of the electrolyte membrane; and a cathodeadjacent to the second side of the electrolyte membrane.